Timing of Syenite Intrusions on the Eastern Slope of the Sredinnyi Range,Kamchatka:Rate of Accretionary Structure Exhumation

摘要

The isotopic thermochronological study included the U-Pb (SHRIMP) and fission-track dating of zircon and fission-track and (U-Th)-He dating of apatite from syenite intrusions cropping out in the eastern slope of the Sredinnyi Range of Kamchatka.The emplacement time of the intrusion was determined,and its exhumation velocity was evaluated.According to U-Pb (SHRIMP) zircon dating,the age of syenite crystallization (63.0+-0.6 and 70.4+-0.7 Ma) corresponds to the Late Cretaceous and Early Paleogene.Starting from 25 Ma,the cooling rate of the intrusion,which was likely controlled by exhumation,varied from 4 deg C/Ma to 20 deg C/Ma.It the geothermal gradient is assumed to be 30 deg C/km,the exhumation rate of the intrusion from the Late Oligocene and until now ranged from 0.18 km/Ma to 0.67 km/Ma.